The present invention relates to an aircraft engine pod with optimized acoustic attenuation.
It is known that the engines fitted to aircraft are sources of noise at a very high level. This is particularly troublesome when the aircraft equipped with these engines is located near to an inhabited area, for example during takeoff or landing. Environmental standards, which are becoming increasingly strict, dictate that the noise level of an aircraft, and therefore the noise level of the engines, be kept below a legislatory threshold so as to limit the noise nuisance suffered by the inhabitants of said area. This legislatory threshold is sometimes reduced further during the night, which means that the noisiest aircraft can then neither land nor take off, which is a constraint, or even a loss of potential income, for the airlines which operate such aircraft. In consequence, it is desirable to reduce the level of acoustic emissions of such an engine to below said regulatory thresholds so as to be able to operate profitably.
It is also known that a great deal of the noise generated by an aircraft engine comes from the fan of the latter arranged in the internal duct of the pod of said engine and that this internal duct consists of a tubular air intake extended, on one side, by a flared air intake peripheral lip and, on the other side, by a tubular transition part connecting it to the casing of said fan and having the main objectives of allowing ease of assembly and disassembly of said air intake and of protecting the latter against wear and foreign object damage resulting from objects sucked in by the fan.
In the known way, there is provided, on the internal surface of said air intake, an acoustic attenuation internal tubular piece, of the resonator type, allowing some of the soundwaves from the fan to be trapped, and thus reducing the level of noise emitted to the outside by the engine.
Such an acoustic attenuation internal tubular piece generally has a cellular-core(s) sandwich structure and, in a known way, may be made as a single piece. However, for ease of construction and fitting, this internal piece is usually made as several shells, each of which forms a longitudinal part of said piece and which are assembled by means of longitudinal fishplates which join the facing lateral edges of adjacent shells together.
Such fishplates generally comprise a longitudinal fishplate strip arranged on the external side of said tubular piece and a longitudinal fishplate strip arranged on the internal side thereof. The internal longitudinal fishplate strips constitute areas of the interior surface of the air intake in which, on the one hand, the noise is not absorbed and, on the other hand, the soundwaves are diffracted, this having the effect of diluting the acoustic energy from near the wall toward the axis of the engine and thus of greatly degrading, in terms of noise level reduction, the performance of said piece by comparison with a monolithic piece.